Pneumatic SS switches - home/limit?

[Swede]

Quite some time ago, I picked up a pneumatically actuated table that uses crossed-roller guides. It also has the neatest little pair of solid state switches mounted so as to limit the travel of the table. They consist of a single fixed magnet, and two sensors which travel with the table. Both switches are completely sealed, making them ideal for a small mill or lathe. These are probably some type of hall effect switch, but it could also be a magnetically-actuated reed relay.

There are no markings at all. Only two leads from the switch sensors, where I expected 3. Before I get really excited about these switches (there are plenty more on eBay), anyone have any insights into them? I'm sure they'd do fine for limit switches, but homing switches require good accuracy.

Finally, has anyone been successful creating their own solid-state switches for home CNC? I did some experiments with a hall sensor (temp. compensated; a nice hall chip) and found that, while reliable, the repeatability was nowhere near that of a standard microswitch, which has worked for me nicely and consistently repeats to about 0.0004" / 0.010mm, usually better.

[Al_The_Man]

Owen, I think what you have is magnet operated reed switches, they are made by Hamlin, I can look up up the part number tomorrow.
Is this the ones? http://canada.newark.com/NewarkWebCo...KU=34C3227&N=4
Al

[Swede]

Hi Al, These (link) are similar to what I have. There is a guy on eBay selling dozens of these, NIB (New In Bag??) Looking at the block circuit, they appear to be hall, but I'm not sure. At the price he's selling them for, I may grab a couple. I'd like to use them for both home switches and possibly some tool length sensing, if I can get good repeatability.

http://www.smcworld.com/2002/bp_e/pdf/2503_040.pdf

[Al_The_Man]

Yes, I believe they are hall effect, SMC make Pneumatic cylinders and they use these to detect the position of the piston, if you notice they mention a bore size actuator as a detector ring has to be fitted to the piston of the Pneumatic non ferrous cyclinder. They can be used in other applications though.
(NIB = New In Box)
Al